DRAINAGE . Ill 



treat more respectfully a lingering scepticism as to the 

 efficacy of deep drains in very retentive soils ; and instead 

 of wondering at this scepticism, we wonder rather that deep 

 thorough-draining has so rapidly made converts. Repre- 

 sentations are made of soils which consist of some inches 

 of a moderately porous material reposing on a subsoil which 

 is said to be impervious ; and we are told that it is of no 

 use to make the drain deeper into the impervious matter 

 than will suffice for laying the conduit. If the subsoil is 

 impervious, as glass or even as cast-iron or caoutchouc are 

 impervious, we at once admit the soundness of the argu- 

 ment. We only want to ask one question Is your subsoil 

 moister after the rains of mid-winter than it is after the 

 drought of midsummer ? if it is, it will drain. Mr. Mechi 

 asks, shrewdly enough, " If your soil is impervious, how 

 did you get it wet?" This imperviousness is always pre- 

 dicated of strong clays plastic clays they are sometimes 

 called. We really thought that no one was so ignorant as 

 not to be aware that clay lands always shrink and crack 

 with drought, and the stiffer the clay the greater the shrink- 

 ing, as brickmakers well know. In the great drought 36 

 years ago, we saw, in a very retentive soil in the Vale of 

 Belvoir, cracks which it was not very pleasant to ride 

 among. This very summer, on land which, with reference 

 to this very subject, the owner stated to be impervious, we 

 put a walking-stick 3 feet into a sun-crack without finding 

 a bottom, and the whole surface was what Mr. Parkes not 

 inappropriately calls a net-work of cracks. When heavy 

 rain comes upon the soil in this state, of course the cracks 

 fill, the clay imbibes the water, expands, and the cracks are 

 abolished. But if there are 4 or 5 feet parallel drains in 

 the land, the water passes at once into them, and is carried 

 off. In fact, when heavy rain falls upon clay lands in this 

 cracked state, it passes off too quickly, without adequate fil- 

 tration. Into the fissures of the undrained soil the roots 

 only penetrate to be perished by the cold and wet of the suc- 

 ceeding winter ; but in the drained soil the roots follow the 

 threads of vegetable mould which have been washed into 



